The exemplary embodiment relates to a printing system. It finds particular application in connection with printing of color and monochrome images by utilizing separate paper delivery pathways which enables components of the printing system not in use at a particular time to be placed in a non-operational mode, and will be described with particular reference thereto. However, it will be appreciated that the embodiment finds application in other systems in which color and monochrome images are rendered.
Electronic printing systems typically employ an input terminal which receives images in digital form and conversion electronics for converting the image to image signals or pixels. The printing system may include a scanner for scanning image-bearing documents or be connected to a computer network which supplies the digital images. The signals are stored and are read out successively to a marking engine for formation of the images and transfer of the images to a print medium, such as paper. Printing systems have been developed which employ multiple marking engines for black, process (or full) color, and custom color (single color or monochrome) printing of selected pages within a print job.
In a typical xerographic marking device, such as a copier or printer, a photoconductive insulating member is charged to a uniform potential and thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the photoconductive insulating surface in exposed or background areas and creates an electrostatic latent image on the member, which corresponds to the image areas contained within the document. Subsequently, the electrostatic latent image on the photoconductive insulating surface is made visible by developing the image with a developing material. Generally, the developing material comprises toner particles adhering triboelectrically to carrier granules. The developed image is subsequently transferred to a print medium, such as a sheet of paper. The fusing of the toner onto paper is generally accomplished by applying heat to the toner with a heated roller and application of pressure. In multi-color printing, successive latent images corresponding to different colors are recorded on the photoconductive surface and developed with toner of a complementary color. Each toner is associated with a separate housing and applied to the paper in sequence. The single color toner images are successively transferred to the copy paper to create a multi-layered toner image on the paper. The multi-layered toner image is then permanently affixed to the copy paper in the fusing process.
Recently, printing systems have been developed which include a plurality of marking engine modules. These systems enable high overall outputs to be achieved by printing portions of the same document on multiple printers. Such systems are commonly referred to as “tandem engine” printers, “parallel” printers, or “cluster printing” (in which an electronic print job may be split up for distributed higher productivity printing by different marking engines, such as separate printing of the color and monochrome pages).
In such machines, color marking engines which print with cyan, magenta, and yellow (CMY) as well as black (K) toners allow printing of both process color and black images on a single marking engine. However, the cost of producing black prints on a color marking engine is often higher than for a dedicated monochrome device. One reason for this is that the color components are often cycled, even during black printing. Although in some systems, the color components can be disabled during the production of monochrome prints, this tends to increase mechanical complexity to provide for retraction of the color components and to disengage their drives. Another reason for the higher cost is that the marking engine may provide a certain interdocument color toner throughput to control toner age in the system.